A variety of stuff is stored within a refrigerator. A large amount of humidity is always kept within the refrigerator. Particularly, since the temperature of a refrigerating chamber of the refrigerator is relatively higher than that of a freezing chamber thereof, microorganisms including mold or bacteria may easily grow in the refrigerating chamber according to the kind, amount, state or the like of stored stuff.
If microorganisms including mold or bacteria grow within the refrigerator as such, freshness of stored stuff is rapidly deteriorated and it is not good in view of hygiene. Further, there is a problem in that inner parts of the refrigerator, for example, selves and vegetable boxes, particularly liners, made of resins are discolored.
To solve this problem in the prior art, i.e. to improve antibiotic and whitening effects, zinc-based or copper-based inorganic antibiotic substances, organic antibiotic substances or the like have been added to resins for manufacture of parts of refrigerators, thereby imparting the antibiotic and whitening effects. In other words, the parts of the refrigerators are produced by extruding the resins for manufacture of the parts to which the antibiotic substances have been directly added.
However, there are the following problems in such a prior art.
First, since conventional antibiotic substances for imparting antibiotic and whitening effects are zinc-based or copper-based substances with high activity, there is a problem in that they are discolored into yellow with time under the influence of light, heat or the like.
Further, since antibiotic substances are mixed directly with resins for manufacturing parts of refrigerators, inorganic zinc-based or copper-based antibiotic substances or organic antibiotic paints, which are relatively expensive, should be directly added in a large amount such as 0.5 to 5% by weight in order to maintain antibiotic capability and the degree of whitening. Thus, there are many problems in view of their costs.
Moreover, in case of conventional liners, resins with antibiotic substances mixed therewith should be extruded at a high temperature of 210 to 250° C. Other parts such as shelves or vegetable boxes should be subjected to injection molding at a temperature of 300° C. or greater. Therefore, organic antibiotic substances that are relatively weak at high temperature may be easily carbonized and thus cannot properly perform their functions. Gas is easily generated during processes, resulting in corrosion on surfaces of liners or parts. Otherwise, the whitening effect is degraded, resulting in the phenomenon of yellowing. In addition, there is a critical problem such as surging during extrusion.
Particularly, since a relatively large amount of antibiotic substances is used, there is a problem in that much failure such as those described above occurs when parts of refrigerators are manufactured by molding resins with the antibiotic substances mixed therewith.